skema soalan final v.2 - bfc315332603
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FINAL EXAMINATION
SEMESTER II
SESSION 2011/2012
COURSE NAME : MECHANICAL & ELECTRICAL SYSTEM
Q1 (a) Discuss on the importance of Mechanical and Electrical System for high
rise building. Give at least three (3) main reasons.(6 marks)
Answer:1. High-speed building vertical transportation helps to conveys peoples/building occupants
from one level to the other levels faster than using stairs in high rise buildings. (2m)
2. High pressure water system is needed to supply water for drinking and cleaning purposesand also as protection against fire at the higher levels. (2m)
3. HVAC system helps to keep the building occupants stays at a comfort level because as thebuilding height increase, it is impossible for the building occupants to rely on natural
ventilation due to high wind pressure at the external environment. (2m)
(b) Explain the process of heat transfer through conduction, convection
and radiation in terms of definition, medium and transfer method.
Conduction Convection Radiation
Medium material liquid/gas vacuum/fluid/gas
Methodmolecular
agitation
fluid
movementby photon
Definition as below as below as below
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(9 marks)
(c) A certain un-insulated cavity wall has a U-value of 0.85W/mK. If
insulation board is added to the construction, where the thickness of
this board is 0.40mm, calculate the percentage reduce for the U-value.
Given that the thermal conductivity of the insulation board is
0.025W/mK.
Step Calculation
Thickness of material, d 0.04m
Thermal conductivity of insulation board, k @ 0.025
k-value of proposed insulating material is k=0.025
Use formula involving thickness of material d, so
the value of Rib
Rib= d/k so,
Rib=0.04/0.025
Rib=1.6
Given R1=1/U1Calculate R1
R1=1/0.85 so,
R1=1.176
Calculate R2 Rib=R2-R1so,
R2= Rib+ R1R2=1.6+1.176
R2=2.776
U-Value U2=1/R2
Calculate proposed U2
U2= 1/2.776
U2= 0.36
Percentage reduce
(U1-U2)/U1x10057.65%
(10 marks)
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When the air supplyis controlled mechanically and the air exhaust takes place on a
natural way by ventilation openings, windows or shafts there will be an overpressure
in the building.
To prevent draught, the air supply in the room has to be placed as high as possibleand
the air inlet grid must have a possibility to be regulated.
By preheating the incoming air draught problems can also be decreased. An air filter
can be usedto clean the incoming air. A ventilator controls the air supply and the
outdoor air is transported into the building by ducts.
Because of the mechanically produced over pressure in the building, the system is less
dependent on the weather conditions than a fully natural ventilation system. By
controlling the ventilator it is possible to control the ventilation capacity of the
system.
In a supply system,a fan pulls outside air into the house, creating positive pressure.
Ductwork brings the air into the living spacesthat need it most typically the
bedrooms and living room.
Balance system
Or
A balanced central system uses two fansand creates a neutral or balanced pressure.
One fan exhausts air out of the house, while the other brings the same amount of
outside air into the house.
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They may be two wall-mounted fansof equal capacity--one for supply and one for
exhaust--in two different rooms.
Alternatively, they may be ducted to supply air to the common living areas, such as
living rooms and bedrooms, and to exhaust air from the rooms where pollution is
high, such as the kitchen and bathroom.
In a balanced system, airis supplied to some rooms and exhausted from others. An
optional heat- or energy-recovery unit transfers heat or humidity from one air stream to
the other. Spot exhaust is included where necessary; here it is in the laundry room
Plenum System
Or
Plenum is the space that can facilitate air circulationfor heating and air conditioning
systems, by providing pathways for either heated/ conditioned or return airflows.
Spacebetween the structural ceiling and the dropped ceiling or under a raised floor istypically considered plenum.
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Population percentage at 5 min peak demand period = 17%
Floor height = 3.3 metres
(6 marks)
1. Flow rate allowing 17% of population
950017 =161.5 persons during 5 min peak demand period10100 (2 Marks)
2. Travel & speed
Assuming floor height of 3.3m, the lift travel = 19 3.3=62.7 From table, thenearest travel for offices is 60m which requires speed of 3.5m/s. (Groundfloor is not included)
(2 Marks)
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3. Number and capacity of lift
From table, for 20-passenger cars may be installed having a handling capacity of165 and interval of 29s (1 Marks)
.4. Quality of service
From table interval 29s ---satisfactory waiting time of 25-35 s (excellent)5 lift / 20 storeys ---satifactoryOr more than 5 lift.
(2 Marks)
(c) Define the following:
(i) Passive fire system
(ii) Active fire system
Then, list down three (3) of the fire hazard categories with example of suitable
fire fighting agents each.(7 marks)
c) Definition:
1) Passive fire systemsPassive fire protection ( pfp ) is defines as protection through ignition delays,
reduced rate of burning and fire spread.
Or
Protections through human indirect approach which more focusing on building
designs or architectural works with the purpose to delay the spreading of fire and
fire exit.
2) Active fire systemsActive fire protection (AFP) is AFP is characterized by items or systems, which
require a certain amount of motion and response in order to work, contrary to
passive fire protection.
4 Fire Hazard categories
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(d) In the fire hydrants system, it consists of using hose reel and riser and
generally the type of riser can be either wet, dry or foam riser. With the
help of sketches, explain how the wet and dry riser works.(8 marks)
d)
Dry riser system Wet riser system
( 1 marks for each sketches)
Dry riser system.
The riser system is maintained in dry condition during non-fire condition.
The riser must always be inspecting to prevent the case of corrosion.
It use direct supply approach where the source of water is from water main pipe
outside the building or hydrants.
Class Type of Fire Fire Fighting Agent
AFires that involve flammable solids such as wood, cloth,rubber, paper, and some types of plastics
Water, Dry Chemical Powder, Foam
B
Fires that involve flammable liquids or liquifiable solidssuch as petrol/gasoline, oil, paint, some waxes &plastics, but notcooking fats or oils AND Fires thatinvolve flammable gases, such as natural gas,hydrogen, propane, butane
CO2, Dry Chemical Powder, Foam,
Halon
C
Fires that involve any of the materials found in Class Aand B fires, but with the introduction of an electricalappliances, wiring, or other electrically energizedobjects in the vicinity of the fire, with a resultantelectrical shock risk if a conductive agent is used tocontrol the fire
CO2, Dry Chemical Powder, Halon
DFires that involve combustible metals, such as sodium,magnesium, and potassium
Dry Chemical Powder
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The riser must be connecting to the outdoor hydrants to get the water.
Usually the system will be activate/ assembled by fire brigade.
This system is slower than wet riser system in providing water.
Wet riser system
It uses indirect supply approach which the source of water is from the storage
tank.
The riser is always filled with water and can be used immediately during fire
occurrence.
Maintenance must be done to check for the leaking pipe.
This system using pump to distribute the water.
The source of water depends on the storage tank capacity.
Q4 (a) Explain briefly the following electrical terms:
(i) Current (I)
An electric current is the flow of electric charges. Conventionally this is the flow of positive charge. In a simple circuit such as that illustrated, the current in the wire is composed of
electrons that flow from the negative pole of the battery (the cathodeat the bottom
of the battery) and return to the positive pole (the anodeat the top of the battery,
marked by a +).
Electric current is the time rate of change of charge, measured in amperes (A). Mathematically, the relationship between current i, charge q, and time t, is Where current is measured in amperes (A), and 1 ampere = 1 coulomb/second
(ii) Voltage (V)
Some work or energy transfer is required to move the electron in a conductor in aparticular direction. This work is performed by an external electromotive force
(emf), typically represented by the battery.
The emf is also known as voltage orpotential difference. Electric potential is the energy required to move a unit of electric charge to a
particular place in a static electric field.
Voltage can be measured by a voltmeter. The unit of measurement is the volt.
(iii) Resistance (R)
Is an internal property of matter that resists the flow of electric current. A material with low resistance to electrical flow is called a conductor. A material with a high resistance to electrical flow is called an insulator: paper
rubber.
Electrical conductors are pure metals; aluminum, copper, silver, gold and platinum.
(6 marks)
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(b) Compare the difference between power and energy in electricity
Power Energy
Power is a measure of how fastenergy is being used. (power is the
rate of consuming energy) Power is a certain amount of energy
used in a certain length of time
P = energy/time = W/t
Power is the time rate of expendingor absorbing energy, measured in
watts (W).
Power is the rate of consumingenergy.
Energy is the fundamental ability todo work and produce action.
Energy exists in many forms, suchas mechanical, sound, light,
electrical, nuclear and chemical.
Energy cannot be created ordestroyed. It can be converted from
one form to another.
Energy is measured in joules, but inmany fields other units, such as
kilowatt-hours and kilocalories, are
customary.
Electrical energy is the most
convenient form of energy that isreadily to be convert to other forms.
For examples; to mechanical energy
through a motor, to lighting energy
through a lamp, and to heating
energy through a resistance heater.
(4 marks)
(c) Suppose that two 100 watts lamp and two 200 watts lamp are plugged
into a 240 volt circuit. The two lamps are connected in parallel. Calculate the
current flow through each lamp, the total current in the circuit, the
total resistance of the circuit, the total energy consumed in a year, and the
cost of electrical energy for the year (based on RM1.10 per kWh). Assuming
that the lamps are used 8 hours per day and 250 days per year. All
calculation steps shall be included in your answer.(15 marks)
Current flow through each lamp (4 marks)
P=IxE, I=P/E
I1=100w/240v=0.416A
I2=100w/240v=0.416A
I3=200w/240v=0.833A
I3=200w/240v=0.833A
Total current through the circuit (2 marks)
IT=0.416 x 2 + 0.833 x 2 = 2.498 A/2.5A
Total resistance of the circuit (5 marks)
R=E/I
*resistance of lamps
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R1=240/0.416=576.9/577ohms
R2=240/0.416=576.9/577ohms
R3=240/0.833=288.1/288ohms
R4=240/0.833=288.1/288ohms
Total resistance of the circuit
1/RT=1/577+1/577+1/288+1/288
1/RT=0.0017+0.0017+0.0035+0.0035 = 0.0104
RT=1/0/0104=96.15ohms
Total energy consumed in a year (2 marks)
W=Pxt = (200+200) x 8 x 250 = 800,000Wh=800kWh.
Cost of electrical energy for the year (2 marks)
Cost=energy used x energy rate=600kWh x RM1.10/kWh=RM660,000 per year.
Q5 (a) As an consultant engineer, you are asked to design water storage tank,
suction tank, and supply pipe for discharge of 1.25litres/sec,
based on gravity supply for Tun Syed Nasir hostel. The hostel are
consists of three (3) blocks of building, each building have 100 rooms
and in each room maximum 4 students can be accommodated. Also
determine the total water requirement for DTI hostel. Assume head
loss is negligible, and length of pipe is 30m allow 20% for bends
and other unforeseen. Assume 91 litres per person of cold water
to cover 24 hours interruption of supply, and disruption of
supply 12 hours.(20 marks)
Answer (a)
Data:
3 building blocks TDI hostel
100 rooms in 1 block of building
4 persons can be accommodated in 1 room
91 lit/day per person per day consumption
Disruption of supply for 12 hours
Effective Length of pipe = 30 m
Discharge of supply pipe = 1.25litres/sec
Head loss = 20% of effective length of pipe
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For practical design assume 4 storage tanks for 1 block of building, therefore each
building block will have to install 3 storage tanks.
Water required to store in 1 tank = 109.33/12 = 9.12 m3
Size of tank is depend upon the choice of student either circular, rectangle, square,however it volume of tank must be greater than the required water volume for storage.
Assume square tank of = 2.1 m x 2.1 m x 3 m (with free board of 0.7m)
o Volume of suction tank = 1/3 x total water requirement
= 1/3 x 164 m3 = 54.66 m3
For practical design assume 3 suction tanks = 54.66/3 = 18.50 m3
Size of tank is depend upon the choice of student either circular, rectangle, square,
however it volume of tank must be greater than the required water volume for storage.
Assume square tank of = 3 m x 3 m x 2.3 m (with free board of 0.3m)
o Diameter of supply pipe can be calculated by Thomas box formula:
(b) Differentiate between water efficiency and water conservation? Enlist
the names of water efficiency approach?(5 marks)
Water efficiency means using improved technologies and practices that deliver equal
or better service with less water. For example, the use of low-flow faucet (A regulator
for controlling the flow of a liquid) aerators can be more powerful than no aerators for
washing hands.
Water conservation has been associated with curtailment of water use and doing
less with less water, typically during a water shortage, such as a drought; for
example, minimizing lawn watering and automobile washing in order to conserve
water. Water conservation also includes day-to-day demand management to better
manage how and when water is used, so it is common to hear the words water
conservation used synonymously with water efficiency.
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Water Efficiency Approach
Rainwater Harvesting (RWH) Water Recycling Water Efficient Irrigation
Water Efficient Fittings Metering and Leak Detection System